I run into a wall when it comes to adding weight. I can rep out a certain weight with full range of motion/scapular retraction/etc for ages, but the minute I add a few pounds I lose range of motion completely. There's no gradual drop-off in the number of "good" reps that I see with other exercises (squats, deads, etc).

I seem to have this same issue too with rows. X#, I can do over and over and over and it looks good, but X+5# and the ROM I can do shrinks dramatically. I don't know exactly what causes the problem but it definitely happens to me. It seems to happen less with the DB rows than with the BB rows or machine rows, so I have stuck more to the DBs, but other than that I don't really know what the deal is.